Abstract: The CdS thin films were prepared on Flexible PI、AZO and ITO substrates by r.f. magnetron sputtering technique,and annealed at 380℃ in CdCl2 and dry air. The morphology, structure and optical properties of all samples were characterized by the scanning electron microscopy, X-ray diffraction and ultraviolet-visible spectroscopy. The results show that the microstructures of all the CdS thin films dependent on the type of substrate by as-deposited and annealed CdS thin films on different substrates, grain recrystallizes, grain size increases significantly and no longer depend on the substrate type. The entire prepared CdS thin films show a mixed phase structure of cubic and hexagonal. After annealing, the proportion of hexagonal phase is increased, the crystallization quality of CdS thin film is improved. The optical transmittance changes obviously after annealing, among them, the optical transmittance of CdS thin film on flexible AZO substrate is over 80%.